Catalyst based on oxides of Fe, Co, Bi and Mo

ABSTRACT

Catalysts of the formula I 
     
          A.sub.a B.sub.b O.sub.x !.sub.p  C.sub.c D.sub.d Fe.sub.e Co.sub.f E.sub.i 
    
      F j  O y  ! q                                    I, 
     where 
     A is bismuth, tellurium, antimony, tin and/or copper, 
     B is molybdenum and/or tungsten, 
     C is an alkali metal, thallium and/or samarium, 
     D is an alkaline earth metal, nickel, copper, cobalt, manganese, zinc, tin, cerium, chromium, cadmium, molybdenum, bismuth and/or mercury, 
     E is phosphorus, arsenic, boron and/or antimony, 
     F is a rare-earth metal, vanadium and/or uranium, 
     a is from 0.01 to 8, 
     b is from 0.1 to 30, 
     c is from 0 to 4, 
     d is from 0 to 20, 
     e is from 0 to 20, 
     f is from 0 to 20, 
     i is from 0 to 6, 
     j is from 0 to 15, 
     x and y are numbers determined by the valency and frequency of the elements other than oxygen in I, and p and q are numbers whose ratio p/q is in the range from 0.001 to 0.099, and a process for the preparation of these catalysts, their use for the ammonoxidation, oxidation or dehydrogenation of ethylenically unsaturated compounds, and a process for the ammonoxidation, oxidation or oxidative dehydrogenation of ethylenically unsaturated compounds in the presence of the novel catalysts.

The present invention relates to catalysts of the formula I

     A.sub.a B.sub.b O.sub.x !.sub.p  C.sub.c D.sub.d Fe.sub.e Co.sub.f E.sub.i F.sub.j O.sub.y !.sub.q                                   I,

where

A is bismuth, tellurium, antimony, tin and/or copper,

B is molybdenum and/or tungsten,

C is an alkali metal, thallium and/or samarium,

D is an alkaline earth metal, nickel, copper, cobalt, manganese, zinc,tin, cerium, chromium, cadmium, molybdenum, bismuth and/or mercury,

E is phosphorus, arsenic, boron and/or antimony,

F is a rare-earth metal, vanadium and/or uranium,

a is from 0.01 to 8,

is b is from 0.1 to 30,

c is from 0 to 4,

d is from 0 to 20,

e is from 0 to 20,

f is from 0 to 20,

i is from 0 to 6,

j is from 0 to 15,

x and y are numbers determined by the valency and frequency of theelements other than oxygen in I, and p and q are numbers whose ratio p/gis in the range from 0.001 to 0.099.

The present invention also relates to a process for the preparation ofthese catalysts, to the use of these catalysts for the ammonoxidation,oxidation or dehydrogenation of ethylenically unsaturated compounds, andto a process for the ammonoxidation, oxidation or oxidativedehydrogenation of othylenically unsaturated compounds in the presenceof the novel catalysts.

EP-A 000 835 describes catalysts having the composition

     M'.sub.m' N'.sub.n' O'.sub.x' !.sub.q'   A'.sub.a' C'.sub.b' D'.sub.c' E'.sub.d' F'.sub.e' N'.sub.f' O'.sub.y' !.sub.p',

where

M' is Bi, Te, Sb, Sn and/or Cu,

N' is Mo and/or W.

A' is an alkali metal, Ti and/or Sm,

C' is Ni, Co, Mn, Mg, Be, Ca, Sr, Ba, Zn, Cd and/or Hg,

D' is Fe, Cr, Ce and/or V,

E' is P, As, B and/or Sb,

F' is a rare-earth metal, Ti, Zr, Nb, Ta, Re, Ru, Rh, Ag, Au, Al, Ga,In, Si, Ge, Pb, Th and/or U.

a' is 0-4,

b' is 0-20,

c' is 0.01-20,

d' is 0-4,

e' is 0-8,

f' is 8-16,

m' is 0.01-10,

n' is 0.1-30,

and x' and y' are numbers determined by the valency and frequency of theelements other than oxygen, and q' and p' are numbers whose ratio q'/p'is in the range from 0.1 to 10.

The component M'_(m') N'_(n') O'_(x') ! is referred to as the key phase,and the component A'_(a') C'_(b') D'_(c') E'_(d') F'_(e') N'_(f')O'_(y') ! is referred to as the guest phase.

Regarding the preparation of these catalysts, EP-A 000 835 recommendspre-forming component M'_(m') N'_(n') O'_(x') ! in the absence of theother constituents, and then mixing it with oxides or water-solublesalts of the elements of the guest phase and, after drying, calciningthe mixture.

EP-A 000 835 furthermore discloses to employ the catalytic compositionsmentioned therein as catalysts for gas-phase-catalytic oxidation oforganic compounds. However, the compositions disclosed in EP-A 000 835have the disadvantages that they do not have entirely satisfactoryactivity and selectivity when used in the gas-phase-catalytic oxidationof organic compounds.

DE-C 33 38 380 discloses catalytically active compositions of theformula II

    Bi.sub.a" W.sub.b" Fe.sub.c" Mo.sub.d" Y.sup.1.sub.e" Y.sup.2.sub.f" Y.sup.3.sub.g" Y.sup.4.sub.h" O.sub.x"                    (II),

where

y¹ is nickel and/or cobalt,

y² is thallium, an alkali metal and/or an alkaline earth metal,

Y³ is phosphorus, arsenic, boron, antimony, tin, cerium, lead and/orniobium,

Y⁴ is silicon, aluminum, zirconium and/or titanium,

d' sic! is 12,

    ______________________________________                                         a'       sic! is from 0.5 to 5                                                                              where a"/b" is                                  b"      is from 0.5 to 4      from 0.1 to 4,                                 ______________________________________                                    

c" is from 0.2 to 5,

e" is from 3 to 10,

f" is from 0.02 to 2,

g" is from 0 to 5,

h" is from 0 to 10, and

x" is a number determined by the valency and frequency of the elementsother than oxygen in II,

which are obtained by first mixing a bismuth compound and a tungstencompound in an aqueous medium, drying the aqueous mixture, calcining theresultant composition at from 600° to 900° C. and subsequently powderingthe product in such a way that the particle size is less than 152 μm,and treating the resultant powder with an aqueous solution of thesources of the other constituents of the composition II, andevaporating, shaping and calcining the resultant mixture.

DE-C 33 38 380 also discloses that the compositions II are suitable ascatalysts for the gas-phase-catalytic preparation of unsaturatedaldehydes by oxidation.

However, the compositions II disclosed in DE-C 33 38 380 have thedisadvantage that they do not have entirely satisfactory activity andselectivity in the ammonoxidation of propene to acrylonitrile.

It is an object of the present invention to provide catalysts which donot have said disadvantages.

We have found that this object is achieved by the catalysts defined atthe outset.

Suitable elements in the novel catalysts are:

A is bismuth, tellurium, antimony, tin and/or copper,

B is molybdenum and/or tungsten,

C is an alkali metal, thallium and/or samarium,

D is an alkaline earth metal, nickel, copper, cobalt, manganese, zinc,tin, cerium, chromium, cadmium, molybdenum, bismuth and/or mercury,

E is phosphorus, arsenic, boron and/or antimony,

F is a rare-earth metal, vanadium and/or uranium,

a is from 0.01 to 8, preferably from 0.1 to 6,

b is from 0.1 to 30, preferably from 0.2 to 8,

c is from 0 to 4, preferably from 0.01 to 3,

d is from 0 to 20, preferably from 0 to 15,

e is from 0 to 20, preferably from 0 to 15,

f is from 0 to 20, preferably from 0 to 15,

i is from 0 to 6, preferably from 0 to 4,

j is from 0 to 15, preferably from 0 to 10.

Preferred catalysts are those which contain at least one of the elementsbismuth, molybdenum and/or tungsten and iron having a stoichiometriccoefficient which is not zero and is preferably ≧0.01.

Furthermore, the novel catalysts I prove to be more advantageous thehigher the percentage of the various chemically different componentshaving a mean particle size (measured using a Sympatec laser diffractioninstrument) in the range from 10 nm to less than 1 μm, preferably in therange from 10 nm to 800 nm, particularly preferably from 10 nm to 600nm.

In particular, particles of the key phase and/or of the guest phase ofthe catalyst preferably have a mean particle size in the range from 10nm to less than 1 μm, particularly preferably in the range from 10 nm to800 nm, very particularly preferably from 10 nm to 600 nm.

The key phase A_(a) B_(b) O_(x) here preferably has the stoichiometry

    Bi.sub.2 W.sub.2 O.sub.9 and/or Bi.sub.2 Mo.sub.2 O.sub.9,

the former being preferred.

The novel compositions are obtainable by the following steps:

(a) preparation of a key phase having the composition A_(a) B_(b) O_(x),

(b) preparation of a guest phase having the composition C_(c) D_(d)Fe_(e) Co_(f) E_(i) F_(j) O_(y) or water-soluble salts of elements ofthe guest phase or a mixture of at least one water-soluble salt of theseelements and at least one calcined phase of one of these elements whichis not in the form of a water-soluble salt, and

(c) mixing of the key phase with the guest phase, and

(d) if desired drying of the mixture obtained in (c), followed bycalcination and, if desired, shaping of the catalyst composition formedin this way in a manner known per se (see EP-A 000 835 and DE-C 33 38380).

In a particular embodiment, at least one of the catalyst components (thekey phase, the precursor thereof, the guest phase or a calcined oxidephase of one of the compounds occurring in the guest phase) iscomminuted by means known per se, for example using a ball mill or byjet grinding, wet comminution being preferred. The mean particle sizeachieved by the comminution is preferably chosen to be in the range from10 nm to less than 1 μm, particularly preferably from 10 nm to 800 nm,very particularly preferably from 10 nm to 600 nm.

The comminuted catalyst component is then usually mixed with theremaining catalyst components, if desired likewise comminuted,preferably in solution or suspension.

The resultant mixture is generally subjected to drying, preferably spraydrying to give a spray material.

The resultant catalyst precursor is then generally calcined at from 400°to 900° C., preferably at from 500° to 800° C., preferably in a streamof air. The calcination is generally carried out for from 0.1 to 20hours.

The catalytically active composition is preferably applied to an oxidicsupport, such as SiO₂, Al₂ O₃, TiO₂ or ZrO₂. In a preferred embodiment,the oxidic support, such as SiO₂ Al₂ 0_(3l), TiO₂ or ZrO₂ is, before thespray drying, mixed lacuna! the mixture of catalyst components, it beingpossible to employ the catalyst prepared in this way directly fororganic syntheses in a fluidized-bed reactor.

Furthermore, the calcined catalyst can be comminuted and shaped in amanner known per se, for example by pressing hollow cylinders orextrudates by methods known per se.

In a further preferred embodiment, the precursor of the key phase, A_(a)B_(b) O_(x) !, is comminuted after calcination, preferably at from 400°to 900° C., usually in a stream of air. The calcination in generallycarried out for from 0.1 to 20 hours.

A very intimate, preferably finely divided, dry mix of the otherconstituents of the novel catalyst desired is generally preparedstarting from sources suitable in a manner known per se (cf. EP-A 835and DE-C 33 38 380) (for example water-soluble salts, such as halides,nitrates, acetates, carbonates or hydroxides, are combined in an aqueoussolution, and the aqueous solution is subsequently spray-dried, orwater-insoluble salts, for example oxides, are suspended in an aqueousmedium and the suspension is subsequently spray-dried); the dry mix isreferred to here as the precursor of the guest phase. The only essentialfeature is that the constituents of the preguest phase are eitheralready oxides or are compounds which can be converted into oxides byheating, if necessary in the presence of oxygen.

The calcined precursor of the key phase and the precursor of the guestphase are subsequently usually mixed with one another in the desiredmixing ratio, preferably compacted by pressing and then expedientlycalcined (normally in a stream of air) at from 400° to 900° C. for anumber of hours.

In the case of unsupported catalysts, the pressing is generally carriedout directly to the desired catalyst geometry, preference being given tohollow cylinders having an external diameter and length of from 2 to 10mm and a wall thickness of from 1 to 3 mm. However, the active catalystsaccording to the invention can also be comminuted after the calcinationand applied to inert supports in order to prepare supported catalysts.The application can also have already been carried out before the finalcalcination. In this case, the application is preferably carried out asdescribed in EP-B 293 859. It is of course also possible to employ thecompositions according to the invention in powder form.

The catalysts according to the invention have, compared withcorresponding catalysts of the prior art, both an increased activity andan increased selectivity for gas-phase-catalytic oxidation of organiccompounds, such as lower (3 to 6 carbon atoms) alkanes, alkanols,alkanals, alkenes and alkenals, to olefinically unsaturated aldehydesand/or carboxylic acids and to the corresponding nitriles(ammonoxidation), in particular of propene to acrylonitrile and ofi-butene or tert-butanol to methacrylonitrile. They are also suitablefor the oxidative dehydrogenation of organic compounds.

EXAMPLES Example 1

(a) Preparation of a key phase

0.5 kg of a solution of Bi(NO₃)₃ in aqueous nitric acid (11% by weightof Bi, 6.4 % by weight of HNO₃, in each case based on the solution) wasmixed with 67 g of H₂ WO₄, and the mixture was stirred at 50° C. for 1hour.

The resultant suspension was spray-dried at 290° C. and calcined at 750°C. for 2 hours. The resultant preformed calcined mixed oxide (Bi₂ W₂ O₉)containing a small amount of WO₃ impurity was subsequentlywet-comminuted to a mean particle size of 400 nm (measured on a Sympateclaser diffraction instrument) by means of a stirred mill, givingsuspension 1 (precursor of key phase 1).

(b) Preparation of a guest phase

A solution of 5.57 kg of ammonium heptamolybdate in 16 l of water wasmixed with a solution containing 3.83 kg of cobalt(II) nitrate and 2.66kg of iron(III) nitrate dissolved in 8 l of 10% strength by weightnitric acid, and with 19.1 kg of an aqueous mixture containing 49% ofits weight of colloidal SiO₂, and 15.4 g of an aqueous solutioncontaining 48% by weight of KOH (suspension 2).

Suspension 1 was subsequently mixed with suspension 2. The mixture wasthen evaporated to dryness by spray drying and subsequently calcined at290° C. for 3 hours, then at 425° C. for a further 3 hours and finallyat 610° C. for a further 3 hours. The resultant catalyst was suitablefor direct use in a fluidized-bed reactor.

The catalyst had the following composition:

     Bi.sub.2 W.sub.2 O.sub.9 ! .sub.0.05  Mo.sub.12 Co.sub.5 Fe.sub.2.5 K.sub.0.05 O.sub.x !

Example 2 Comparative catalyst (analogous to Example 1 of EP-A 000 835)

Example 1 was repeated, but with the difference that the precursor ofthe key phase was employed directly after spray drying without priorcomminution.

Example 3 Ammonoxidation of propene

(a) A propene/ammonia/air/water gas mixture in the volume ratio1/1.3/10/4.7 was reacted at 450° C. in a fixed-bed reactor. The contacttime (volume (gas)/volume-(catalyst) per unit time) was 4.5 seconds. Thecatalyst employed was the catalyst from Example 1.

(b) Example 3(a) was repeated using the with sic! catalyst from Example2.

The results of the ammonoxidation are shown in the table below.

                  TABLE                                                           ______________________________________                                                   Propene conversion                                                                           Yield   Selectivity                                 Catalyst    %!             mol %!  %!                                         ______________________________________                                        Example 1  98.5           85.8    87.1                                        for comparison                                                                           98.1           82.2    83.8                                        Example 2                                                                     ______________________________________                                    

We claim:
 1. A catalyst of the formula I

    (A.sub.a B.sub.b O.sub.x).sub.p (C.sub.c D.sub.d Fe.sub.e Co.sub.f E.sub.i F.sub.j O.sub.y).sub.q                                    I,

where A is bismuth, tellurium, antimony, tin and/or copper, B ismolybdenum and/or tungsten, C is an alkali metal, thallium and/orsamarium, D is an alkaline earth metal, nickel, copper, cobalt,manganese, zinc, tin, cerium, chromium, cadmium, molybdenum, bismuthand/or mercury, E is phosphorus, arsenic, boron and/or antimony, F is arare-earth metal, vanadium and/or uranium, a is from 0.01 to 8, b isfrom 0.1 to 30, c is from 0 to 4, d is from 0 to 20, e is from 0 to 20,f is from 0 to 20, i is from 0 to 6, j is from 0 to 15,x and y arenumbers determined by the valency and frequency of the elements otherthan oxygen in I, and p and q are numbers whose ratio p/q is in therange from 0.001 to 0.099, obtained by the following steps (a)preparation of a key phase having the composition A_(a) B_(b) O_(x), (b)preparation of a guest phase having the composition C_(c) D_(d) Fe_(e)Co_(f) E_(i) F_(j) O_(y) or water-soluble salts of elements of the guestphase or a mixture of at least one water-soluble salt of the elements ofthe guest phase and at least one calcined phase of one of the elementsof the guest phase which is not in the form of a water-soluble salt, and(c) mixing of the key phase with the guest phase, and (d) optionallydrying the mixture obtained in (c), optionally drying the mixtureobtained in (c), optionally followed by calcination and optionallyfollowed by shaping of the catalyst compositionthe mean particle size ofat least one of a guest phase or a key phase composition being in therange from 10 nm to less than 1μm.
 2. A catalyst as defined in claim 1,wherein the catalyst has been applied to an oxidic support material. 3.A process for the preparation of a catalyst as defined in claim 1 inwhich a key phase and a guest phase are prepared, the two phases aremixed and subsequently, the mixture of these phases is calcined, whereinthe key phase has the composition A_(a) B_(b) O_(x) and the guest phasehas the composition C_(c) D_(d) Fe_(e) Co_(f) E_(i) F_(j) O_(y).
 4. Aprocess for the ammonoxidation, oxidation or oxidative dehydrogenationof ethylenically unsaturated compounds wherein the process is carriedout using a catalyst as defined in claim 1.